On Wed, Sep 07, 2022 at 02:23:58AM +0200, Ben Hutchings wrote:
> > > - The added mitigation, for PBRSB, requires removing any RET
> > > instructions executed between VM exit and the RSB filling. In these
> > > older branches that hasn't been done, so the mitigation doesn't work.
> >
> > I checked 4.19 and 5.4, I don't see any RET between VM-exit and RSB
> > filling. Could you please point me to any specific instance you are
> > seeing?
>
> Yes, you're right. The backported versions avoid this problem. They
> are quite different from the upstream commit - and I would have
> appreciated some explanation of this in their commit messages.
Ahh right, I will keep in mind next time.
> So, let's try again to move forward. I've attached a backport for 4.19
> and 5.4 (only tested with the latter so far).
I am not understanding why lfence in single-entry-fill sequence is okay
on 32-bit kernels?
#define __FILL_ONE_RETURN \
__FILL_RETURN_SLOT \
add $(BITS_PER_LONG/8), %_ASM_SP; \
lfence;
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